The present invention relates to the structure of an electronic semiconductor device in particular comprising at least one integrated circuit and power components integrated monolithically on the same chip of semiconductor material.
The association in the same silicon chip of high voltage power transistors with a vertical current flow from the emitter to the collector and an integrated control circuit provides a very compact and efficient device which is economical to produce and which satisfies current industrial requirements.
A device of this type, disclosed in the Italian Patent Application 6616 A/84 of Aug. 21, 1984 in the name of the applicants, involves the use of planar junctions with a very high breakdown voltage thereby enabling the device to be used in high voltage power applications.
The high voltage arrangement of P-N planar junctions is achieved by means of a stepped profile and a concentration of impurities in one of the two sides of the junction which decreases from the center to the periphery with a predetermined extension.
The device constructed in this way is not, however, able to operate correctly during switching. In effect, since there are several regions of opposite types of conductivity within the chip, parasitic bipolar transistors are produced. These are not disadvantageous when the high voltage planar junctions of the device are reverse biased since in this case both the emitter-base and collector-base junctions of the parasitic transistors are reverse biased. They are, however, damaging when the power transistors, controlled by the integrated circuit, are brought into the saturation state. In this case the firing of parasitic elements which inject current into the isolation region, which has within it the integrated circuit, causes the forward biasing of the internal P-N junction existing on the boundary of the integrated circuit of the device with the surrounding isolation region when the threshold voltage of 0.6 V of the junction is exceeded. This leads to the loss of the electrical isolation and consequently causes incorrect operation and may even lead to the destruction of the integrated circuit of the device.